Bone treatment systems and methods

ABSTRACT

The invention provides instruments and methods for prophylactic treatment of an osteoporotic vertebral body or for treating a vertebral compression fracture (VCF). In one exemplary method, a probe system uses a high speed rotational cutter for abrading or cutting a plane within vertebral cancellous bone. Optional irrigation and aspiration sources are included in the probe system for removing abraded bone debris. In one embodiment, the high speed cutter uses a tissue-selective abrading surface that abrades or cuts bone but does not cut soft tissue. After the creation of a weakened cut plane in the bone, reduction of the fracture requires reduced forces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Provisional U.S. Patent ApplicationSer. No. 60/629,628 filed Nov. 19, 2004 titled Systems and Methods forTreating Vertebral Fractures. This application also is related to U.S.application Ser. No. 11/165,652 filed Jun. 24, 2005 titled BoneTreatment Systems and Methods; and U.S. patent application Ser. No.11/165,651 filed Jun. 24, 2005, titled Bone Treatment Systems andMethods. The entire contents of all of the above cross-referencedapplications are hereby incorporated by reference in their entirety andshould be considered a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to medical devices, and more particularlyto methods and apparatus for treating an abnormal vertebra. Moreparticularly, an apparatus and method includes using a probe carrying atissue-selective elastomeric rotational cutter having an abrasivesurface for cutting a plane within vertebral cancellous bone to create aweakened plane.

2. Description of the Related Art

Osteoporotic fractures are prevalent in the elderly, with an annualestimate of 1.5 million fractures in the United States alone. Theseinclude 750,000 vertebral compression fractures (VCFs) and 250,000 hipfractures. The annual cost of osteoporotic fractures in the UnitedStates has been estimated at $13.8 billion. The prevalence of VCFs inwomen age 50 and older has been estimated at 26%. The prevalenceincreases with age, reaching 40% among 80-year-old women. Medicaladvances aimed at slowing or arresting bone loss from aging have notprovided solutions to this problem. Further, the affected populationwill grow steadily as life expectancy increases. Osteoporosis affectsthe entire skeleton but most commonly causes fractures in the spine andhip. Spinal or vertebral fractures also have serious consequences, withpatients suffering from loss of height, deformity and persistent painwhich can significantly impair mobility and quality of life. Fracturepain usually lasts 4 to 6 weeks, with intense pain at the fracture site.Chronic pain often occurs when one level is greatly collapsed ormultiple levels are collapsed.

Postmenopausal women are predisposed to fractures, such as in thevertebrae, due to a decrease in bone mineral density that accompaniespostmenopausal osteoporosis. Osteoporosis is a pathologic state thatliterally means “porous bones”. Skeletal bones are made up of a thickcortical shell and a strong inner meshwork, or cancellous bone, ofcollagen, calcium salts and other minerals. Cancellous bone is similarto a honeycomb, with blood vessels and bone marrow in the spaces.Osteoporosis describes a condition of decreased bone mass that leads tofragile bones which are at an increased risk for fractures. In anosteoporotic bone, the sponge-like cancellous bone has pores or voidsthat increase in dimension, making the bone very fragile. In young,healthy bone tissue, bone breakdown occurs continually as the result ofosteoclast activity, but the breakdown is balanced by new bone formationby osteoblasts. In an elderly patient, bone resorption can surpass boneformation thus resulting in deterioration of bone density. Osteoporosisoccurs largely without symptoms until a fracture occurs.

Vertebroplasty and kyphoplasty are recently developed techniques fortreating vertebral compression fractures. Percutaneous vertebroplastywas first reported by a French group in 1987 for the treatment ofpainful hemangiomas. In the 1990's, percutaneous vertebroplasty wasextended to indications including osteoporotic vertebral compressionfractures, traumatic compression fractures, and painful vertebralmetastasis. In one percutaneous vertebroplasty technique, bone cementsuch as PMMA (polymethylmethacrylate) is percutaneously injected into afractured vertebral body via a trocar and cannula system. The targetedvertebrae are identified under fluoroscopy. A needle is introduced intothe vertebral body under fluoroscopic control to allow directvisualization. A transpedicular (through the pedicle of the vertebrae)approach is typically bilateral but can be done unilaterally. Thebilateral transpedicular approach is typically used because inadequatePMMA infill is achieved with a unilateral approach.

In a bilateral approach, approximately 1 to 4 ml of PMMA are injected oneach side of the vertebra. Since the PMMA needs to be forced intocancellous bone, the technique requires high pressures and fairly lowviscosity cement. Since the cortical bone of the targeted vertebra mayhave a recent fracture, there is the potential of PMMA leakage. The PMMAcement contains radiopaque materials so that when injected under livefluoroscopy, cement localization and leakage can be observed. Thevisualization of PMMA injection and extravasion are critical to thetechnique—and the physician terminates PMMA injection when leakage isevident. The cement is injected using small syringe-like injectors toallow the physician to manually control the injection pressures.

Kyphoplasty is a modification of percutaneous vertebroplasty.Kyphoplasty involves a preliminary step that comprises the percutaneousplacement of an inflatable balloon tamp in the vertebral body. Inflationof the balloon creates a cavity in the bone prior to cement injection.Further, the proponents of percutaneous kyphoplasty have suggested thathigh pressure balloon-tamp inflation can at least partially restorevertebral body height. In kyphoplasty, it has been proposed that PMMAcan be injected at lower pressures into the collapsed vertebra since acavity exists to receive the cement—which is not the case inconventional vertebroplasty.

The principal indications for any form of vertebroplasty areosteoporotic vertebral collapse with debilitating pain. Radiography andcomputed tomography must be performed in the days preceding treatment todetermine the extent of vertebral collapse, the presence of epidural orforaminal stenosis caused by bone fragment retropulsion, the presence ofcortical destruction or fracture and the visibility and degree ofinvolvement of the pedicles. Leakage of PMMA during vertebroplasty canresult in very serious complications including compression of adjacentstructures that necessitate emergency decompressive surgery.

Leakage or extravasion of PMMA is a critical issue and can be dividedinto paravertebral leakage, venous infiltration, epidural leakage andintradiscal leakage. The exothermic reaction of PMMA carries potentialcatastrophic consequences if thermal damage were to extend to the duralsac, cord, and nerve roots. Surgical evacuation of leaked cement in thespinal canal has been reported. It has been found that leakage of PMMAis related to various clinical factors such as the vertebral compressionpattern, and the extent of the cortical fracture, bone mineral density,the interval from injury to operation, the amount of PMMA injected andthe location of the injector tip. In one recent study, close to 50% ofvertebroplasty cases resulted in leakage of PMMA from the vertebralbodies. See Hyun-Woo Do et al, “The Analysis of PolymethylmethacrylateLeakage after Vertebroplasty for Vertebral Body Compression Fractures”,Jour. of Korean Neurosurg. Soc. Vol. 35, No. 5 (May 2004) pp. 478-82,(http://www.jkns.or.kr/htm/abstract.asp?no=0042004086).

Another recent study was directed to the incidence of new VCFs adjacentto the vertebral bodies that were initially treated. Vertebroplastypatients often return with new pain caused by a new vertebral bodyfracture. Leakage of cement into an adjacent disc space duringvertebroplasty increases the risk of a new fracture of adjacentvertebral bodies. See Am. J. Neuroradiol. 2004 February; 25(2): 175-80.The study found that 58% of vertebral bodies adjacent to a disc withcement leakage fractured during the follow-up period compared with 12%of vertebral bodies adjacent to a disc without cement leakage.

Another life-threatening complication of vertebroplasty is pulmonaryembolism. See Bernhard, J. et al., “Asymptomatic diffuse pulmonaryembolism caused by acrylic cement: an unusual complication ofpercutaneous vertebroplasty”, Ann. Rheum. Dis. 2003; 62:85-86. Thevapors from PMMA preparation and injection are also cause for concern.See Kirby, B., et al., “Acute bronchospasm due to exposure topolymethylmethacrylate vapors during percutaneous vertebroplasty”, Am.J. Roentgenol. 2003; 180:543-544.

Another disadvantage of PMMA is its inability to undergo remodeling—andthe inability to use the PMMA to deliver osteoinductive agents, growthfactors, chemotherapeutic agents and the like. Yet another disadvantageof PMMA is the need to add radiopaque agents which lower its viscositywith unclear consequences on its long-term endurance.

In both higher pressure cement injection (vertebroplasty) andballoon-tamped cementing procedures (kyphoplasty), the methods do notprovide for well controlled augmentation of vertebral body height. Thedirect injection of bone cement simply follows the path of leastresistance within the fractured bone. The expansion of a balloon alsoapplies compacting forces along lines of least resistance in thecollapsed cancellous bone. Thus, the reduction of a vertebralcompression fracture is not optimized or controlled in high pressureballoons as forces of balloon expansion occur in multiple directions.

In a kyphoplasty procedure, the physician often uses very high pressures(e.g., up to 200 or 300 psi) to inflate the balloon which first crushesand compacts cancellous bone. Expansion of the balloon under highpressures close to cortical bone can fracture the cortical bone, orcause regional damage to the cortical bone that can result in corticalbone necrosis. Such cortical bone damage is highly undesirable andresults in weakened cortical endplates.

Kyphoplasty also does not provide a distraction mechanism capable of100% vertebral height restoration. Further, the kyphoplasty balloonsunder very high pressure typically apply forces to vertebral endplateswithin a central region of the cortical bone that may be weak, ratherthan distributing forces over the endplate.

There is a general need to provide systems and methods for use intreatment of vertebral compression fractures that provide a greaterdegree of control over introduction of bone support material, and thatprovide better outcomes. Embodiments of the present invention meet oneor more of the above needs, or other needs, and provide several otheradvantages in a novel and non-obvious manner.

SUMMARY OF THE INVENTION

The invention provides systems and methods for treatment of vertebralcompression fractures as well as systems and methods for prophylactictreatment of osteoporotic vertebrae in subjects having vertebrae thatare susceptible to a compression fracture. The invention also can beused in correcting and supporting bones in other abnormalities such asbone tumors and cysts, avascular necrosis of the femoral head and tibialplateau fractures.

In one embodiment, a probe system is provided that has a working endcomprising an elastomeric abrasive cutter that is rotated at high speedsby a motor drive. The rotational elastomeric abrader has atissue-selective abrading surface that within a selective rpm range canabrade or cut cancellous bone or cortical bone but will not cut softtissue. The system is used for abrading or cutting at least one path orspace within vertebral cancellous bone. Irrigation and aspirationsources are included in the probe system for removing abraded bonedebris. After the creation of a path or space in bone, an in-situhardenable bone cement volume is introduced into each path or space tosupport the vertebra.

In another embodiment of the invention, a probe system has a working endthat comprises an expandable structure having an abrasive surface. Inuse, the expandable abrading surface is rotated at high speed to cutbone while being expanded to increase the cross section of the path orspace being created. The use of the expandable cutter allows thetreatment of bone with low pressures to create paths or spaces withoutexplosive expansion forces known in prior art balloon procedures thatare designed to crush and compact cancellous bone in a vertebra.

There is a general need to provide systems and methods for use intreatment of vertebral compression fractures that provide a greaterdegree of control over introduction of bone support material, and thatprovide better outcomes. The present invention meets this need andprovides several other advantages in a novel and nonobvious manner.

These and other objects of the present invention will become readilyapparent upon further review of the following drawings andspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to better understand the invention and to see how it may becarried out in practice, some preferred embodiments are next described,by way of non-limiting examples only, with reference to the accompanyingdrawings, in which like reference characters denote correspondingfeatures consistently throughout similar embodiments in the attacheddrawings.

FIG. 1 is a perspective schematic view of an exemplary system of theinvention with an elastomeric tissue-discriminating cutter for abradingand cutting bone in an abnormal vertebra.

FIG. 2A is a sectional view of a vertebra with an elastomeric cuttersimilar to that of FIG. 1 being advanced over a straight guide member toabrade a path in cancellous bone.

FIG. 2B is a sectional view of an abnormal vertebra with anotherflexible shaft elastomeric cutter similar to that of FIG. 1 beingadvanced over at least one curved shape memory guide member to abrade aplurality of paths in cancellous bone.

FIG. 3 is a view of the abnormal vertebra of FIG. 2B with the pluralityof path in cancellous bone infilled with a hardenable bone cement toreinforce the vertebra.

FIG. 4A is a sectional view of another vertebra with a flexible shaftelastomeric cutter similar to that of FIGS. 1 and 2B being used toabrade cortical bone to create a weakened plane.

FIG. 4B is a side view of the vertebra of FIG. 4A showing the method ofabrading and cutting holes in cortical bone to create a weakenedcortical bone region.

FIG. 5 is a sectional view of another vertebra showing a method of usingthe elastomeric cutter of FIG. 1 to abrade and cut a plane in cancellousbone of a vertebra.

FIG. 6 is a perspective schematic view of the working end andelastomeric abrasive cutter of an alternative embodiment wherein thecutter is expandable in transverse section.

FIG. 7 is a sectional view of an alternative working end and elastomericabrasive cutter that is expandable in transverse section.

FIG. 8 is a sectional view of an alternative working end with afluid-expanded elastomeric abrasive cutter that is expandable intransverse section.

FIGS. 9A-9D are sequential views of an fluid-expandable elastomericcutter being used to abrade a space in cancellous bone, for example, ina vertebra.

FIG. 10A is a perspective view of an alternative working end with firstand second rotatable abrasive cutter portions that are configured toextend in a plane relative to the instrument axis to create a weakenedplane in bone.

FIG. 10B is a view of the working end of FIG. 10A in a method of use toabrade and cut a weakened plane in a vertebral cancellous bone.

FIG. 11 is a cut-away of an alternative flexible cutter as if takenalong line 11-11 of FIG. 10A.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic view of an exemplary bone cutting system or probe100 that has handle portion 102 that transitions to elongated extensionmember 104 that extends along axis 105. The extension member 104 carriesa distal working end 110 that comprises a high speed elastomeric,abrasive rotational cutter indicated at 112. The handle portion 102 canbe any suitable assembly for gripping with a human hand and can carrytrigger and actuator mechanisms known in the art.

In the embodiment of FIG. 1, the elastomeric abrasive cutter 112 isfixedly coupled to the distal end of elongated drive member 114 that isrotated at a high speed by a rotation mechanism, such as an air motor orelectric motor indicated at 115. The drive member 114 rotates in bore118 in an elongated rigid sleeve 120 that is coupled to handle portion102. The elongated sleeve 120 and elastomeric cutter 112 are configuredwith dimensions suited for insertion into a vertebra from a posteriortranspedicular or extrapedicular approach, with the diameter of thesleeve 120 and cutter 112 ranging between about 1.0 mm and 4.0 mm, andmore preferably between 1.5 mm and 3.0 mm. The length of the cutter 112ranges from 1 mm to 10 mm, and more preferably from 2 mm to 5 mm. Ofparticular interest, the elastomeric cutter 112 is fabricated of aresilient polymer (e.g., silicone or urethane) that is embedded withabrasive crystals 122 or the like, for example diamond or other similarparticles having a mean cross-section ranging between about 1 micron and100 microns, and more preferably between about 5 microns and 50 microns.The rotation mechanism or motor 115 is configured for rotating theelastomeric cutter 112 at speed ranging from about 500 rpm to 400,000rpm, and more preferably at speeds ranging between about 5,000 rpm and100,000 rpm.

In the embodiment of FIG. 1, the drive member 114 has a bore 128therethrough that allows the probe 100 to be advanced over a guidemember such as a wire (not shown). The bore 128 also optionally can beused for fluid infusion to irrigate the site, and for this reason afluid source 140 is shown in FIG. 1. As also shown in FIG. 1, the probeor system 100 optionally includes a negative pressure source 145operatively connected to bore 118 in sleeve 120 for aspirating fluid andabraded bone debris from the bone treatment site. The distal end portionof sleeve 120 can have ports 148 or openings therein to allow fluid andbone debris to be aspirated into bore 118 of sleeve 120.

The elastomeric cutter 112 can be operated within a selected speed rangethat preferentially abrades and cuts bone such as cancellous or corticalbone but will not abrade soft tissue. This aspect of the invention isuseful, for example, in operations in the interior of a vertebral body,for example when cutting through a cortical wall and inadvertentlycontacting soft tissue outside the vertebra. The system willdiscriminate tissue density and not cut the lower density soft tissuesuch as ligaments. The use of a resilient cutter at selected speeds todiscriminate in cutting harder tissue and sparing softer tissue wasdisclosed in U.S. Pat. Nos. 4,445,509 and 4,990,134 to David C. Auth,which are incorporated herein by this reference. The Auth patents relateto endovascular catheter tips that are abrasive for cutting occlusivematerials that clog an artery. The present invention is fabricated inthe configuration of a rigid probe 100 with dimensions suited forpercutaneous insertion into an abnormal vertebra.

In one method of use shown in FIGS. 2A and 2B, an elastomeric cutter 112similar to the embodiment shown in FIG. 1 can be used to cut one or morestraight or curved paths in cancellous bone 149 in vertebral body 150.In FIG. 2A, cutter 112 is advanced over a selected straight guide member152. FIG. 2B illustrates cutter 112 advanced over a curved shape memoryalloy guide member 154. In this embodiment, the bore 128 in drive member114 is dimensioned to slide and rotate relative to the guide member 152or 154. In the embodiment of FIG. 2B, the drive member 114 can be ahelical drive element or braided sleeve that is flexible for rotatingthe cutter 112. In FIGS. 2A-2B, a plurality of paths 155 can be cut orabraded by this means with the result shown in FIG. 3. In FIG. 3, theplurality of paths 155 are then filled with a bone cement 158 (e.g.,PMMA) injected through introducer sleeve 159. The bone cement 158 isadapted to prophylactically treat a vertebra 150 that may be susceptibleto a compression fracture.

In FIGS. 4A-4B, another use of elastomeric cutter 112 is shown whereintip 160 of the cutter is penetrated through the cortical bone wall 162of vertebra 150 in at least one location 164 to create a weakenedregion. This use of the cutter will provide a fracturable region or line165 in the cortical bone (FIG. 4B) that will allow for elevation ofvertebral endplate 166 a relative to endplate 166 b upon the pressurizedintroduction of bone fill materials. This use of cutter 112 as indicatedin FIGS. 4A-4B is adapted for cases in which a vertebral compressionfracture has healed in a collapsed position with the bone portionsfusing together. The cutter 112 thus allows cutting through corticalbone 162 with the cutter abrading bone but discriminating tissue basedon density differences so that the cutter does not cut the ligaments 168as the cutter tip 160 penetrates cortical bone layer 162. (FIG. 4A).This method of creating a weakened plane or region 165 in cortical bonewas disclosed by the authors in U.S. Provisional Patent Application Ser.No. 60/622,209 filed Oct. 26, 2004 titled Systems and Methods forTreating Vertebral Fractures, which is incorporated herein by thisreference and made a part of this specification.

FIG. 5 depicts another use of elastomeric cutter 112 in a vertebrawherein the working end 110 of the probe 100 is moved laterally and/ortranslated axially while rotating the elastomeric cutter 112 to abradeand cut a plane P. It can be understood that the cutting can be donefrom one or more access paths to the interior of the vertebra 150 to cuta suitable plane P. After cutting plane P, a bone fill material (e.g.,PMMA) can be introduced in the plane P and increasing injectionpressures of the bone fill material can be used to apply forces to movethe endplates apart to reduce the fracture.

FIG. 6 depicts another probe 180 with an elastomeric cutter 112 similarto that of FIG. 1. In this embodiment, the motor-driven drive member 184also functions as a pull-rod to axially compress and move theelastomeric cutter 112 to the shape indicated at 112′ wherein thetransverse section of the cutter is increased to thereby abrade or cut alarger diameter path in cancellous bone. In this embodiment, the cutter112 can be an elastomeric monolith of silicone, urethane or the likethat is bonded to drive member 184. It can be understood that theproximal end 186 of cutter 112 will be pushed against the distal end 188of sleeve 120 to thereby outwardly expand the transverse section of themonolith. In the embodiment of FIG. 6, a central bore in the probe isnot shown as in bore 128 in FIG. 1, but such a feature is optional.

FIG. 7 is a sectional view of another probe 190 with an elastomericcutter 112 that is similar to that of FIG. 6. In the embodiment of FIG.7, the motor-driven drive member 184 again functions as a pull-rod toactuate elastomeric cutter 112 to an enlarged transverse section. Inthis embodiment, the cutter 112 is hollow to allow greater expansionthan the version of FIG. 6. It can be seen that elastomeric cutter 112has first and second ends, 191 a and 191 b, that are bonded to first andsecond collars 192 a and 192 b that cooperate with drive shaft 184. Thesecond collar is bonded to shaft 184 and the first collar includedprojecting key elements 194 that slide in key slots 196 to key therotation of cutter 112 to that of the shaft 184. In all other respects,the system operates as described above. In another embodiment (notshown) the wall 198 of the elastomeric cutter 112 has a plurality ofperforations and the interior opening communicates with aspiration portsin a hollow drive shaft and/or in the introducer sleeve. It can beeasily understood that an aspiration source and irrigation source as inprobe 100 of FIG. 1 can be incorporated into a system using amechanically expandable elastomeric cutter 112 having a perforated wall.

FIG. 8 is a perspective sectional view of an alternative probe 200 thatcarries a rotatable elastomeric cutter 112 that is fluid expandable, forexample, by inflow of a liquid or a gas from any suitable pressuresource 210. The elastomeric cutter 112 has a substantially thickexpandable wall 212 that carries diamond abrasives as describedpreviously. The expandable wall is coupled to shaft 220 having a lumen232 extending therethrough to deliver fluid from the pressurized source210 to a chamber 242 in the expandable cutter 112. The shaft 220 can bea flexible polymer, a superelastic alloy or the like. As describedpreviously, the probe can have a bore extending therethrough (not shown)for advancing over a straight or curved guide member. A plurality ofdifferently shaped guide members can be used as shown in FIGS. 2B and 3to create varied geometry paths.

In another embodiment similar to that of FIGS. 7 and 8, an expandable,elastomeric cutter 112 can be a resilient polymer without an inflationchamber that is expanded by centrifugal forces resulting from very highrotational speeds, for example 50,000 rpm or higher and can be driven byan air motor. In another embodiment, the wall of a similar balloonstructure is expandable but can still be fluid-permeable to allowleakage of saline or sterile water into the bone being abraded. Anaspiration source can be coupled to such a working end as describedabove.

FIGS. 9A-9D illustrate an alternative method wherein a fluid-expandablestructure with an abrasive surface as in FIGS. 7 and 8 is used to createa space 240 (or multiple spaces) in cancellous bone 149 to receive avolume of bone cement. On aspect of the method includes abrading a spacein a bone and injecting bone cement under high pressure to distractcortical endplates to restore vertebral height. In one embodiment, thebone cement is the type described in co-pending U.S. application Ser.Nos. 11/165,651 and 11/165,652 filed Jun. 24, 2005, both titled BoneTreatment Systems and Methods, wherein the bone cement can be altered inviscosity on demand with the application of energy to prevent cementextravasion.

The method of FIGS. 9A-9D provides safe means for creating a space 240in a bone, for example a substantially large space in vertebralcancellous bone to receive a bone cement. In one prior art method knownas kyphoplasty as described above the section titled “Description of TheRelated Art”, a balloon is inserted in a cut or fractured path incancellous bone 149 and then inflated with very high pressures. Wheninflating such a balloon, the bone structure acts akin to any ceramicmaterial and only fractures under very large loads (e.g. up to 300 psior more in the balloon)—at which time the fracture of cancellous bone isexplosive. In kyphoplasty, the balloon is entirely constrained by thesmall path in cancellous bone until ever-increasing pressure fracturesthe cancellous bone resulting in “explosive” expansion of the balloon.The explosive expansion of a kyphoplasty balloon can cause point loadingwhere the balloon contacts the cortical endplates of the vertebra. Theexplosive expansion of the balloon can easily crack an endplate if theexpanded balloon wall is in close proximity to the endplate. Whenimaging the use of such a balloon device, it has been observed that theballoon moves explosively from a substantially collapsed condition to afully expanded condition in an interval of less than a fraction of asecond—the interval believed to be less than about one tenth of asecond.

In contrast, the method of the invention depicted in FIGS. 9A-9D it isbelieved for the first time performs “non-explosive” balloon expansionwith the interior of a vertebra by configuring the fluid-expandablestructure with high speed rotational abrading functionality. At the sametime, the inventive system removes bone debris by means of irrigationand aspiration to prevent the crushing and compaction of cancellousbone. The fluid-expandable structure 112 of FIGS. 9A-9C can beconfigured with an pressure source and controller so that the expandablestructure is expanded with (i) constant pressure inflows, (ii) constantvolume inflows, (iii) a modulated inflow rate or (iv) pulsed inflows tomove the expandable structure 112 from a non-expanded condition to anexpanded condition over an interval greater than about one tenth of asecond. More specifically, the method includes moving the structure 112from a non-expanded condition to an expanded condition over an intervalranging between about 1/10 of a second and 10 minutes, and morepreferably between about 1 second and 5 minutes; and more preferablybetween about 10 seconds and 2 minutes.

In another aspect of the method of FIGS. 9A-9C, the system uses acontroller to expand the expandable structure 112 to a first increasedtransverse dimension (while rotationally abrading bone) and thenexpansion forces are terminated with the structure partiallyexpanded—followed by at least one other interval to expand the structureto a second transverse dimension and then termination of expansion againwhile rotationally abrading bone. This method further insures that noexplosive expansion forces are applied within a vertebral body as occurswith a kyphoplasty-type balloon and method. Stated another way, themethod of the present invention allows for expansion of structure 112 ina plurality of intervals to increased dimensions that are a fraction ofthe most-expanded shape of the expandable structure 112 (FIGS. 9A-9C).For example, the expandable structure 112 can be expanded to 10%-50% ofits maximum working volume after which inflows are terminated. Then thestructure can be expanded to 20%-60% of its maximum working volumefollowed by a non-expansion interval, then the structure can be expandedto 30%-70% of its working volume followed by a non-expansion interval,and so forth. During the above steps of the method, the controller canrotate the structure 112 at a selected rpm or a varied rpm within theranges described above.

In another aspect of the apparatus and method depicted in FIGS. 8 and9A-9C, the system uses fluid expansion to move an expandable structurefrom a first transverse dimension to a second greater transversedimension in cancellous bone of a vertebra at low non-explosive fluidinflow pressures while rotationally abrading the cancellous bone. Thepressures can be less than 100 psi, or more preferably less than 50 psi,or more preferably less than 25 psi. The system pressures used by theinventive method are far lower than practiced in balloon proceduresadapted to crush and compact cancellous bone.

In one aspect, a method of the invention comprises inserting anexpandable structure into cancellous bone, and expanding the structureat a selected rate of expansion without compacting the cancellous boneby rotation of an abrasive surfaced structure to thereby cut bone. Inanother aspect of the invention, the method of the invention includesinserting an expandable structure into cancellous bone, and expandingthe structure step-wise to insure that explosive expansion does notoccur together with the rotational bone abrading step. In another aspectof the invention, the method includes inserting an expandable structureinto cancellous bone, and expanding the structure with fluid inflowpulses that range from 1 Hz to 1,000 Hz to enhance bone abrasion withthe surface of the expandable structure. More preferably, the fluidinflows are pulses in the range of 10 to 100 Hz.

In one aspect, the apparatus of the invention for abrading bonecomprises (a) an elongated member having a first end and a second end,(b) the second end having an expandable cross-section with an abrasivesurface, and (c) a rotational drive mechanism coupled to the first endfor rotation thereof to abrade a path or a space in a bone. In anexemplary embodiment, the abrasive surface is a polymeric material withabrasive particles affixed thereto, such as diamond particles. Thediamond particles can be natural monocrystalline diamond, syntheticmonocrystalline diamond, polycrystalline diamond or a combinationthereof. The diamond particles have a mean dimension ranging from about1.0 micron to 100 microns.

FIGS. 10A and 10B illustrate another cutting system and method forcutting a plane P in bone to assist in reducing a vertebral fracturethat has healed to some extent. FIG. 10A depicts a bone cutting system200 with introducer 210 that extends along axis 215 to working end 220that includes first and second flexible rotational abrading (cutting)elements 222 a and 222 b. The system includes a rotation mechanism 225in a handle (not shown) of the device such as an electric motor forrotating the rotational elements 222 a and 222 b. Each rotationalelement 222 a and 222 b has a proximal end 224 a and 224 b that iscoupled to the motor drive and extends through a sleeve 226 a and 226 bin the introducer 210. As described above, the rotational elements 222 aand 222 b can be flexible metal wires, braided wires or braid-reinforcespolymeric members. The system 200 further includes a reciprocatingactuator member 240 for outward flexing of the distal end of therotational elements 222 a and 222 b as shown in FIG. 10A. As can be seenin FIG. 10A, the distal ends 242 a and 242 b of the rotational elementsare rotatable and secured in collar 244 that is coupled to actuatormember 240. Still referring to FIG. 10A, it can be seen that the cutter200 can be introduced into a bone in a reduced cross-sectionalconfiguration with the cutting elements 222 a and 222 b in a linearconfiguration (phantom view). It further can be seen that simultaneousrotation of the cutting elements 222 a and 222 b and actuation byactuator member 240 will allow outward cutting in a plane in cancellousbone. FIG. 10B illustrates a method of use wherein the system is used tocut a more-or-less horizontal or sagittal plane P in the cancellous boneand can further be used to abrade cortical bone. Thus, the cuttingsystem 200 can be used to create a weakened plane in the bone forenhancing the application of forces in vectors more-or-lessperpendicular to the cut plane. Irrigation and aspiration can be usedwith the cutting system 200. The application of forces can be created bythe inflow of a bone cement, by injection of graft material, by theexpansion of a balloon, the injection of filler material into a knit,woven or braided structure or sac, or the use of a mechanical jackingsystem.

In the embodiment of FIG. 10A, the cutting elements 222 a and 222 b areindicated as flexible rotating members. In order to make the cuttingelements 222 a and 222 b flex more controllably in the desired plane,further structure can be added to the working end as indicated in FIG.11 which is a cut-away schematic view of a transverse section of theflexible portion of cutter 222 a (see FIG. 10A). In the embodiment ofFIG. 11, a rotatable sleeve 221 a rotates around a flexible rodindicated as a flexible rectangular support member 245. The rectangularsupport member 245 is less adapted to deflect in use since the member245 does not rotate. Other similar non-rotating support members can beused that are eternal to the rotatable sleeve 221 a and coupled to thesleeve by flanges.

In any of the above methods, the volume of bone cement volume cancomprise a PMMA, monocalcium phosphate, tricalcium phosphate, calciumcarbonate, calcium sulphate and hydroxyapatite, or any combinationthereof. The bone cement also can carry allograft material, autograftmaterial or any other infill bone infill granular material or scaffoldmaterial as in known in the art.

The above description of the invention intended to be illustrative andnot exhaustive. A number of variations and alternatives will be apparentto one having ordinary skills in the art. Such alternatives andvariations are intended to be included within the scope of the claims.Particular features that are presented in dependent claims can becombined and fall within the scope of the invention. The invention alsoencompasses embodiments as if dependent claims were alternativelywritten in a multiple dependent claim format with reference to otherindependent claims.

What is claimed is:
 1. A bone treatment device, comprising: an elongated assembly having a working end carrying one or more flexible rotatable members having an abrasive surface surrounding a non-rotatable shaft, the non-rotatable shaft being moveable between a first linear shape and a second curved shape during operation of the rotatable member; and a rotation mechanism operatively coupled to the flexible rotatable member; wherein the abrasive surface is configured to rotate about an axis defined by the non-rotatable shaft when in either of the linear or curved shapes.
 2. The bone treatment device of claim 1 further comprising an actuation mechanism for moving the flexible member between the first linear shape and the second curved shape.
 3. The bone treatment device of claim 1 wherein the rotation mechanism is capable of rotating the flexible member at from 500 rpm to 400,000 rpm.
 4. The bone treatment device of claim 1 further comprising a fluid source coupled to a lumen in the elongated assembly.
 5. The bone treatment device of claim 1 further comprising an aspiration source coupled to a lumen in the elongated assembly.
 6. The bone treatment device of claim 1 further comprising a controller for controlling the rotation of the one or more flexible members.
 7. The bone treatment device of claim 1, wherein the elongated assembly further comprises a rigid sleeve operatively coupled to a handle portion.
 8. The bone treatment device of claim 1, wherein the abrasive surface is a polymer embedded with abrasive crystals.
 9. The bone treatment device of claim 8, wherein the polymer further comprises silicone or urethane.
 10. The bone treatment device of claim 8, wherein the abrasive crystals further comprise diamond or other functionally similar particles having a mean cross-section ranging between 1 micron and 100 microns.
 11. The bone treatment device of claim 1, wherein the rotation mechanism further comprises an air motor.
 12. The bone treatment device of claim 1, wherein the rotation mechanism further comprises an electric motor.
 13. The bone treatment device of claim 1, wherein the non-rotatable shaft has a rectangular cross-section.
 14. The bone treatment device of claim 1, wherein the one or more flexible rotatable members comprises two flexible rotatable members.
 15. The bone treatment device of claim 14, wherein the two flexible rotatable members are configured to actuate to move from a generally linear parallel configuration to a curved configuration, wherein the two curves form a plane and the device is configured to cut along the plane.
 16. The bone treatment device of claim 14, wherein the two flexible rotatable members rotate in opposite directions to cut bone along a plane.
 17. The bone treatment device of claim 1, wherein the abrasive surface is configured to selectively cut tissue so that it can cut cancellous bone but not soft tissue.
 18. A bone cutting system comprising: one or more flexible elongate members comprising: a rotational abrading element; and a non-rotational flexible support element passing through the rotational abrading element and moveable from a first linear shape to a second curved shape along a designated plane; and a rotation mechanism configured to rotate the rotational abrading element about the non-rotational flexible support element; wherein the rotation of the rotational abrading element and biasing of the non-rotational flexible support element toward the second curved shape is configured to cut bone substantially along the designated plane.
 19. The bone cutting system of claim 18, wherein the non-rotational flexible support element is configured to bias the flexible elongate member towards movement from the first shape to the second shape along the designated plane.
 20. The bone cutting system of claim 18, wherein the rotational abrading element comprises a sleeve surrounding the non-rotational flexible support element.
 21. The bone cutting system of claim 18, further comprising a reciprocating actuator member configured to flex the one or more flexible elongate members outward from the first linear shape to the second curved shape.
 22. The bone cutting system of claim 18, wherein the flexible elongate members comprise two flexible elongate members.
 23. The bone cutting system of claim 22, wherein the two flexible elongate members rotate in opposite directions to cut bone along the designated plane.
 24. The bone cutting system of claim 18, wherein one or more flexible elongate members are configured to selectively cut tissue so that it can cut cancellous bone but not soft tissue.
 25. A cutting device comprising: a rotation mechanism; an introducer; two or more flexible cutting elements connected to the rotation mechanism at a proximal end and passing through the introducer, the flexible cutting elements comprising: a rotatable sleeve; and a flexible non-rotating support member within the rotatable sleeve, wherein the rotatable sleeve is configured to rotate about the support member; a reciprocating actuator member for outward flexing of distal ends of the two or more flexible cutting elements; and a collar coupled to the reciprocating actuator member, the two or more flexible cutting elements secured at the distal ends by and configured to rotate within the collar.
 26. The cutting device of claim 25, wherein the support member is biased towards flexing the flexible cutting element in a particular direction.
 27. The cutting device of claim 25, wherein the introducer having a sleeve through which each flexible cutting element passes.
 28. The cutting device of claim 25, wherein each flexible rod of the two or more flexible cutting elements has a rectangular cross-section. 